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The present invention relates to a projection-type headlamp in which the disposition of a shade member and a light source are determined in such a manner that the luminous utilization efficiency of the headlamp is optimized for given values of the diameter and focal distance of a projection lens.
A vehicular headlamp must be designed to illuminate the forward view of the driver so that driving at night can be safely conducted. At the same time, design considerations such as styling, shape, size and the like are also important. For instance, as lamp designs have become more diversified, headlamps have been developed which can have an elongated, rounded or other desired shape. A reduced-height headlamp has been particularly in high demand because it can assist in reducing air resistance of the vehicle by reducing the height of the front end of the vehicle while providing a sporty image to the vehicle design. Also, as shown in FIG. 15, if the height h of the lamp is sufficiently small, it becomes possible to arrange a pair of the lamps above the wheel wells of the vehicle, allowing the vehicle to be designed compactly with a small front overhang (the distance FO from the vehicle front end to the front axle, as indicated in FIG. 15).
In general, as the height of a lamp is reduced, the available luminous flux decreases in proportion to the reduction in height because the available area of the reflector is decreased. Because the vertical portion of a reflector normally contributes to the formation of a diffused light distribution pattern on both sides of the vehicle, if the height of the lamp is reduced, the diffused light is reduced in intensity, reducing the light illuminating the edge of the road or the near range, resulting in a reduction of visibility in the proximity of the vehicle.
A projection-type lamp, which includes an ellipsoidal reflector, a shade and a projection lens, can be employed where the permissible height of the lamp is limited because the allowable area of the reflector is not significantly affected by the reduction in height.
However, if the available height is severely restricted, the diameter of the projection lens (convex lens) of a projection-type lamp must be reduced, and the available light cannot be used efficiently, especially if the focal point of the reflector or other components is not modified.
Generally, it is possible to increase the utilization efficiency by changing the shape and design of the reflector, which though is difficult to achieve on a trial and error basis.
Therefore, it is an object of the present invention to provide a projection-type headlamp in which the position of the shade member or light source is set so that the luminous utilization efficiency of the headlamp is optimized, taking into account any height restrictions imposed on the design of the lamp.
In order to solve the problems mentioned above, the present invention provides a method for optimizing the luminous utilization efficiency of a projection-type headlamp having a given lens diameter and focal distance of the projection lens including the steps of determining the luminous utilization efficiency of the projection-type headlamp with respect to all or a part of the reflecting surface of the reflector of the headlamp as a function of a first focal distance and a second focal distance of the reflector, and also determining characteristics of the diffusion angle in the vertical light direction as functions of the the first focal distance and the second focal distance, thereafter determining the luminous utilization efficiency corresponding to the first focal point and the second focal point for a specified value of the diffusion angle, and determining the first focal distance and the second focal distance where the luminous utilization efficiency is a maximum.
The luminescent portion of the light source is positioned at the first focal point, and a reflector or reflective section where the upper edge portion of the shade member is positioned at or near the second focal point is provided.
The present invention is particularly appropriate for the design of a headlamp of smaller width because the position of the shade member and light source can be set so that the luminous utilization efficiency with respect to the available height is best.